As a reciprocating cutting tool that is driven by a driving source such as electric motor, a saber saw has been known. As well known, the saber saw reciprocates a reciprocating shaft (hereinafter, referred to as a plunger) having a substantially linear saw blade (hereinafter, referred to as a blade) mounted at a leading end thereof, thereby cutting wood, steel, pipe and the like by the blade.
An example of a structure of a related-art saber saw is shown in FIG. 7 (see, for example, JP-A-2002-79417). FIG. 7 is a sectional view showing an entire saber saw 101 according to the related-art technology. A motor 7 is embedded in a motor housing 2 made of resin and a handle 3 is connected to a rear part of the motor housing 2. In the handle 3 having a D shape when in a side view, a switch 4 that controls power feed to the motor 7 is embedded. When a trigger 4 a is pulled, the motor 7 is rotated. An inner cover 5 and gear cover 6 made of metal and accommodating a power transfer means are provided at the front of the motor housing 2. The motor housing 2 and a front cover 26 configure a housing of the invention. A part of an outer side of the housing is provided with the front cover 26 made of an electrical insulating and heat insulating elastic member having a large frictional coefficient. A base 25 for pressing and stabilizing the saber saw 101 body to a material to be cut upon a cutting operation is attached to a leading end-side corresponding to the front of the gear cover 6 so that it can be advanced and retreated. Upon the cutting operation, it is possible to stabilize the saber saw 101 by pushing the base 25 against the material to be cut.
A driving gear 8 is configured integrally with or by a separate member from a leading end of a motor shaft 7a. Rotation movement of the motor shaft 7a is converted into reciprocating movement of a plunger 120 by a movement converting part. The plunger 120 holds a blade 27 via a blade holder (blade holding unit) 23 at a front end portion of and reciprocates the blade 27 forward and backward, thereby cutting the material to be cut. The blade holder 23 is configured such that attach and detach of the blade 27 can be realized by one touch by operating a rotatable knob 24. The blade 27 can be mounted to the blade holder in an upper-lower reverse direction. The movement converting part that converts the rotation movement of the motor 7 into the reciprocating movement of the plunger 120 in the forward and backward direction includes a second shaft 9 that is provided in parallel with the motor shaft 7a, a driven gear 10 that is attached to the second shaft 9 so as not to be rotatable, a first inclined shaft part 9a that is provided at the front of the second shaft 9 and is provided with a predetermined angle relative to a shaft center of the driven gear 10, a second inclined shaft part 9b that has an opposite phase to the first inclined shaft part 9a and is provided with a predetermined angle relative to the shaft center of the driven gear 10, and a first reciprocating plate 18 and a second reciprocating plate 33 that are attached to the respective inclined shaft parts via bearings 17, 32.
As the driven gear 10 is engaged with the driving gear 8, the rotation of the electric motor 7 is decelerated with a predetermined reduction ratio and the second shaft 9 is rotated (deceleration unit). The rotation movement of the second shaft 9 is transferred as the rotation movement of the first inclined shaft part 9a and rotates the first reciprocating plate 18, which is held at the inclined shaft part by two bearings 17, and a sub shaft 11, which is provided to be concentric with the shaft center of the driven gear 10. A leading end of an oscillating shaft part 18a of the first reciprocating plate 18 is formed with a spherical part 18b. The spherical part 18b is positioned in an opening 120b of the plunger 120 and is rollably engaged in the opening with a slight gap. As the second shaft 9 is rotated, the first reciprocating plate 18 is moved forward and backward. Therefore, the plunger 120 is reciprocated forward and backward by the spherical part 18b that is positioned at an upper end of the first reciprocating plate 18 and in the opening 120b of the plunger 120. The plunger 120 is arranged inside a guide sleeve 113 attached to the gear cover 6 and is supported to an inside of a first bearing metal 19 attached to the guide sleeve 113 so that it can reciprocatingly slide in an axial direction. The first bearing metal 19 is a substantially cylindrical sliding bearing (or plain bearing) and an outer periphery thereof is fixed to the guide sleeve 113 and an inner periphery thereof slides with an outer peripheral surface of the plunger 120.
In the meantime, the exterior of the plunger 120 is provided with a balance weight 31 that is engaged with a portion of the plunger 120 and reciprocates forward and backward in an opposite phase to the plunger 120. The balance weight 31 is moved in the axial direction (front-rear direction) by the second reciprocating plate 33. The second reciprocating plate 33 is held at the second inclined shaft part 9b having a predetermined angle relative to the shaft center of the driven gear 10 via the bearings 32. As the second shaft 9 is rotated, the second reciprocating plate 33 is moved forward and backward in the opposite phase to the first reciprocating plate 18, thereby reciprocating the balance weight 31. The reciprocating movement of the balance weight 31 is configured to have an opposite phase to the plunger 120 enabling an inversion movement (movement having a phase difference of 180°).
In the saber saw 101, the plunger 120 slides inside the first bearing metal 19 and the guide sleeve 113. However, a large diameter part 120c of the plunger 120 and a fitting part of the guide sleeve 113 are not in a complete non-contact state and may partially contact upon the sliding. Thus, wearing and heat generation inevitably occurs, which becomes an obstacle in prolonging a lifespan of the saber saw. Also, in order to prolong the lifespan and to improve the rigidity of the saber saw, it is considered to enlarge the first bearing metal 19 (to lengthen the first bearing metal 19 in the axial direction). However, in this case, it is necessary to increase an axial length (front-rear length) of the guide sleeve 113 so as to be able to accommodate the enlarged first bearing metal 19. As a result, the saber saw 1 body is enlarged.